Multiple bicycle rear sproket assembly

ABSTRACT

A multiple bicycle rear sprocket assembly includes first and second sprockets. The first sprocket includes a plurality of first sprocket teeth. The first sprocket teeth include at least one first tooth having a first maximum axial width for engaging with an outer link plate of the chain, and at least one second tooth having a second maximum axial width for engaging with an inner link plate of the chain. The first maximum axial width is larger than the second maximum axial width. The second sprocket includes a plurality of second sprocket teeth. The second sprocket is smaller than the first sprocket. The second sprocket teeth have additional second teeth only. The additional second teeth are configured for engaging with the inner link plate of the chain. The first maximum axial width is larger than a maximum axial width of each of the additional second teeth.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 15/357,369, filed on Nov. 21, 2016, which is acontinuation application of U.S. patent application Ser. No. 14/053,630,filed on Oct. 15, 2013, now U.S. Pat. No. 9,701,364, issued Jul. 11,2017. This application claims the benefit of U.S. ProvisionalApplication No. 61/824,568, filed on May 17, 2013. The entiredisclosures of U.S. Provisional Application No. 61/824,568 and U.S.patent application Ser. Nos. 14/053,630 and 15/357,369 are herebyincorporated herein by reference.

BACKGROUND Field of the Invention

This invention generally relates to a multiple bicycle rear sprocketassembly including the bicycle sprocket.

Background Information

Bicycle sprockets are provided both to a crank assembly located in themiddle of a bicycle and to the rear wheel, and the rotation of the crankassembly is transmitted to the rear wheel by a chain meshed with thesprockets. In a bicycle chain, an inner link plate and an outer linkplate are linked alternately; therefore, when the teeth of the sprocketshave the same thickness, the gaps between the outer link plate and theteeth of the sprockets are larger than the gaps between the inner linkplate and the teeth of the sprockets. In view of this, there areconventionally known sprockets (Specification of U.S. Pat. No.4,174,642, for example) in which the axial width of the teeth (the teeththickness), relative to the rotational center axis direction of thesprocket, is designed such that the axial width of the teeth meshingwith the outer link plate is larger than the axial width of the teethmeshing with the inner link plate. A conventional sprocket has teeththat taper diametrally outward. It is thereby unlikely that the gapsbetween the sprocket and chain will become smaller and that the chainwill separate from the teeth of the sprocket.

A multiple bicycle rear sprocket assembly comprises a plurality ofsprockets. Among such multiple bicycle sprocket assemblies, one knownexample is a bicycle crank assembly in which a plurality of sprocketshaving different numbers of teeth are mounted to a crank arm. Thesprockets are provided for shifting, and the chain is moved by aderailleur between the two or more sprockets having different numbers ofteeth to perform the shifting action.

SUMMARY

A sprocket having teeth that have different axial widths relative to therotational center axis direction of the sprocket is a structure forpreventing the chain from easily separating from the teeth of thesprocket. Therefore, when a sprocket having teeth that have differentaxial widths, the shifting action becomes complicated.

A problem of the present invention is to make the shifting action easierin a multiple bicycle rear sprocket assembly having teeth that havedifferent axial widths.

In one aspect of the invention, a multiple bicycle rear sprocketassembly includes a first sprocket and a second sprocket. The firstsprocket includes a first sprocket body, a plurality of first sprocketteeth, and at least one first shifting area. The first sprocket teethare disposed along a circumferential direction on a radially outer sideof the first sprocket body. The first sprocket teeth include at leastone first tooth and at least one second tooth. The at least one firsttooth has a first maximum axial width for engaging with an outer linkplate of the chain. The at least one second tooth has a second maximumaxial width for engaging with an inner link plate of the chain. Thefirst maximum axial width is larger than the second maximum axial width.The second sprocket includes a second sprocket body and a plurality ofsecond sprocket teeth. The second sprocket is smaller than the firstsprocket. The second sprocket teeth are disposed along a circumferentialdirection on a radially outer side of the second sprocket body. Thesecond sprocket teeth are configured from additional second teeth only.The additional second teeth are configured for engaging with the innerlink plate of the chain. The first maximum axial width is larger than amaximum axial width of each of the additional second teeth.

Also, other objects, features, aspects and advantages of the presentinvention will become apparent to those skilled in the art from thefollowing detailed description, which, taken in conjunction with theannexed drawings, discloses preferred embodiments of the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the attached drawings which form a part of thisoriginal disclosure:

FIG. 1 is a front view of a bicycle crank assembly according to thefirst embodiment;

FIG. 2 is a front perspective view of the first sprocket;

FIG. 3 is a rear view of the first sprocket;

FIG. 4 is a partial rear perspective view of the first and secondsprockets;

FIG. 5 is a partial side view of the first sprocket, the secondsprocket, or the third sprocket as seen from the radially outer side;

FIG. 6 is a front perspective view of the second sprocket;

FIG. 7 is a front view of the bicycle crank assembly according to thesecond embodiment; and

FIG. 8 is a surface view of the third sprocket.

DETAILED DESCRIPTION OF EMBODIMENTS

Selected embodiments will now be explained with reference to thedrawings. It will be apparent to those skilled in the bicycle field fromthis disclosure that the following descriptions of the embodiments areprovided for illustration only and not for the purpose of limiting theinvention as defined by the appended claims and their equivalents.

In FIG. 1, a bicycle crank assembly (referred to as a crank assemblybelow) 10 according to the first embodiment of the present inventioncomprises a crank arm 12, and a first sprocket 14 and second sprocket 16which are bicycle sprockets according to an embodiment of the presentinvention. The first sprocket 14 and the second sprocket 16 are frontsprockets that can engage with a chain 2. The second sprocket 16 hasfewer teeth than the first sprocket 14. The chain 2 has an outer linkplate 2 a and an inner link plate 2 b.

Crank Arm

The crank arm 12 is integrally and rotatably linked to a crankshaft 19.The crank arm 12 has a sprocket attachment part 20, and an arm part 22provided either integrally to or separate from the sprocket attachmentpart 20.

The sprocket attachment part 20 has a plurality (e.g. four) of sprocketattachment arms 24 disposed at intervals in the circumferentialdirection. The circumferential intervals of the sprocket attachment arms24 may be equal intervals but may also be unequal intervals. In thefirst embodiment, the sprocket attachment arms 24 are disposed at equalintervals and are slanted upstream in advancing rotational direction Rof the crank arm 12 relative to the radial direction. The sprocketattachment arms 24 have first attachment parts 24 a for attaching thefirst sprocket 14. The first attachment parts 24 a are formed in thedistal ends of the sprocket attachment arms 24. The sprocket attachmentarms 24 have second attachment parts 24 b for attaching the secondsprocket 16. The second attachment parts 24 b are formed farther inwardin the radial direction than the first attachment parts 24 a. The firstattachment parts 24 a and the second attachment parts 24 b areconfigured from through-holes, for example, or screw holes or the likethrough which nothing else passes. In the first embodiment, the firstattachment parts 24 a are configured from through-holes, and the secondattachment parts 24 b are configured from screw holes through whichnothing else passes. The first sprocket 14 is fixed to the firstattachment parts 24 a by first fixing bolts 26. The second sprocket 16is fixed to the second attachment parts 24 b by second fixing bolts 28(see FIG. 4).

The arm part 22 is formed either integrally with or separate from thesprocket attachment part 20. In the first embodiment, the arm part 22 isconfigured integrally with the sprocket attachment part 20. The arm part22 has a pedal attachment part 22 a in which a pedal (not shown) can bemounted in the distal end, and a linking hole 22 b to which thecrankshaft 19 is integrally and rotatably linked in the proximal end.

First Sprocket

The first sprocket 14 has a rotational center axis X, and comprises afirst sprocket main body 30, a plurality (e.g. 30 to 60) of teeth 32disposed along the circumferential direction on the radially outer sideof the first sprocket main body 30, and a first shifting area 34, asshown in FIGS. 2 to 5. The first sprocket main body 30 is an example ofa sprocket main body. The first shifting area 34 is an example of ashifting area. The term “shifting area” in the present invention meanseither an area where the chain engages with the teeth of a largesprocket during an up shifting action from a small sprocket to a largesprocket, or an area where the chain separates from the teeth of thelarge sprocket during a down shifting action from the large sprocket tothe small sprocket. The first sprocket main body 30 and the teeth 32 aremade of metal and are formed integrally. The first sprocket main body 30has a plurality (e.g. four) of first fixed parts 30 a fixed to the firstattachment parts 24 a of the sprocket attachment arms 24 and disposed atintervals in the circumferential direction. In the first embodiment, thefirst fixing parts 30 a are configured from through-holes, and aredisposed in positions facing the plurality of first attachment parts 24a. The first sprocket 14 is fixed to the sprocket attachment arms 24 bythe first fixing bolts 26 and a nut member (not shown) threaded with thefirst fixing bolts 26.

There are thirty-six of the teeth 32 in the first embodiment, forexample. The teeth 32 include at least one first tooth 32 a having afirst maximum axial width W1 (see FIG. 5), and at least one second tooth32 b having a second maximum axial width W2. The first teeth 32 a areformed to be capable of engaging with an outer link plate 2 a of thechain 2. The second teeth 32 b are formed to be capable of engaging withan inner link plate 2 b of the chain 2. The first maximum axial width W1is greater than the second maximum axial width W2. The first maximumaxial width W1 of the first teeth 32 a is in a range of preferably 2.5mm or greater and 5.4 mm or less, and more preferably in a range of 3.0mm or greater and 4.5 mm or less. When the first maximum axial width W1of the first teeth 32 a is in such a range, the first teeth 32 a readilywith the outer link plate 2 a without engaging with the inner link plate2 b. The second maximum axial width W2 of the second teeth 32 b ispreferably in a range of 1.5 mm or greater and 2.3 mm or less. When thesecond maximum axial width W2 of the second teeth 32 b is in such arange, the second teeth 32 b have the necessary rigidity and readilyengage with the inner link plate 2 b.

The first teeth 32 a are preferably formed into a + (plus) shape as seenfrom the radially outer side, as shown in FIGS. 2 to 5. The second teeth32 b are preferably formed into a − (minus) shape as seen from theradially outer side. The first teeth 32 a and the second teeth 32 b areformed tapering so as to gradually decrease in axial width toward theradially outer side. The first teeth 32 a and the second teeth 32 bthereby engage more readily with the outer link plate 2 a and the innerlink plate 2 b. Among the plurality of first teeth 32 a, first teeth 32a 1 and first teeth 32 a 2, which are shifting teeth 32 c describedhereinafter, are formed into T shapes as seen from the radially outerside in the first embodiment, as shown in FIG. 2. The first teeth 32 a 1are shifting teeth 32 c for down shifting wherein the chain 2 moves fromthe first sprocket 14 to the second sprocket 16, and the first teeth 32a 2 are shifting teeth 32 c for up shifting wherein the chain 2 movesfrom the second sprocket 16 to the first sprocket 14. In the firstembodiment, the first maximum axial width of the T-shaped first teeth 32a 1, 32 a 2 is less than the first maximum axial width W1 of the +shaped first teeth 32 a, and greater than the second maximum axial widthW2 of the − shaped second teeth 32 b.

At least some of the first teeth 32 a and the second teeth 32 b aredisposed alternately in the circumferential direction, i.e. adjacent toeach other, and in the first embodiment all of these teeth are disposedin this manner as shown in FIG. 2.

The first shifting area 34 includes the first shifting teeth 32 c, whichare provided to at least one of the teeth 32. The first shifting teeth32 c are an example of shifting teeth. In the first embodiment, aplurality (e.g. four) of first shifting teeth 32 c is provided. Thefirst shifting teeth 32 c are provided between the linked first teeth 32a 1 and second teeth 32 b. The first shifting area 34 includes a firstprotuberance 36 a and a second protuberance 36 b, which are formed so asto be capable of supporting the chain 2. The first protuberance 36 a andthe second protuberance 36 b are an example of protuberances.Furthermore, the first shifting area 34 includes a concave part 38disposed farther diametrally inward than the roots of the teeth 32. Thebase portions 32 e correspond to the radially innermost portions of theteeth 32.

The first shifting teeth 32 c have first guide surfaces 32 d for guidingthe chain 2 in a first surface 14 a (see FIG. 2) side and a secondsurface 14 b (see FIG. 3) side of the first sprocket 14, as shown inFIGS. 2 and 3. The first guide surfaces 32 d are an example of a guidesurface. The first surface 14 a of the first sprocket 14 is the frontsurface disposed on the axially outer side farther from the bicycleframe when the crank assembly 10 is mounted to the bicycle. The secondsurface 14 b is the rear surface disposed on the axially inner sidenearer to the bicycle frame. The first guide surfaces 32 d are formed asbeing recessed so as to gradually decrease in thickness toward the sidesof the first shifting teeth 32 c.

The first protuberance 36 a is provided protruding in the second surface14 b of the first sprocket main body 30 in order to guide the chain 2 tothe teeth 32 of the first sprocket 14. The second protuberance 36 b isprovided protruding in the second surface 14 b of the first sprocketmain body 30 in order to guide the chain 2 to the first protuberance 36a. In the first embodiment, the first protuberance 36 a and the secondprotuberance 36 b are provided as a pair (a plurality) spaced atintervals in the circumferential direction. The first protuberance 36 aguides the chain to the second teeth 32 b, which are shown by hatchingin FIG. 3 and are upstream from the first protuberance 36 a in theadvancing rotational direction R of the bicycle crank assembly 10.

The distance L1 between the first protuberance 36 a and the secondprotuberance 36 b is greater than the longitudinal length L2 of theouter link plate 2 a and/or the inner link plate 2 b of the chain 2, asshown in FIG. 1. The distance L1 between the first protuberance 36 a andthe second protuberance 36 b may also be either equal to thelongitudinal length L2 of the outer link plate 2 a and/or the inner linkplate 2 b of the chain 2, or less than the longitudinal length L2. Thefirst protuberance 36 a and the second protuberance 36 b are “swaged”securely to the first sprocket 14 by being plastically deformed. In thepresent embodiment, the first protuberance 36 a is larger in diameterthan the second protuberance 36 b.

The concave part 38 is formed in order to make it easier for the chain 2supported on the first protuberance 36 a to engage with the teeth of thefirst sprocket 14, as shown in FIGS. 3 and 4. Therefore, the concavepart 38 is disposed in proximity to the first protuberance 36 a andfarther diametrally (radially) inward than the base portion 32 e of theteeth 32. In the first embodiment, the concave part 38 is disposeddownstream from the first protuberance 36 a in the advancing rotationaldirection R, and is formed recessed into a substantially triangularshape which inclined upstream (clockwise in FIG. 3) from the diametrallyinner side to the outer side. The chain 2 is thereby readily supportedon the first protuberance 36 a.

Second Sprocket

The second sprocket 16 has a rotational center axis Y, and comprises asecond sprocket main body 40, and a plurality (e.g. 20 to 40) of teeth42 disposed along the circumferential direction on the radially outerside of the second sprocket main body 40, as shown in FIGS. 4 and 6. Thesecond sprocket main body 40 is an example of a sprocket main body. Asecond shifting area 44 is an example of a shifting area. The secondsprocket main body 40 and the teeth 42 are made of metal and are formedintegrally. The second sprocket main body 40 has a plurality (e.g. four)of second fixed parts 40 a fixed to the second attachment parts 24 b(see FIG. 1) of the sprocket attachment arms 24 and disposed atintervals in the circumferential direction. The second fixed parts 40 aare configured from through-holes, and are disposed in positions facingthe plurality of second attachment parts 24 b. The second sprocket 16 isfixed to the sprocket attachment arms 24 by the second fixing bolts 28(see FIG. 4) threaded with the second attachment parts 24 b.

The teeth 42 include at least one third tooth 42 a having a thirdmaximum axial width W3 (see FIG. 5), and at least one fourth tooth 42 bhaving a fourth maximum axial width W4. The third teeth 42 a are formedso as to be capable of engaging with the outer link plate 2 a of thechain 2. The fourth teeth 42 b are formed so as to be capable ofengaging with the inner link plate 2 b of the chain 2. The third maximumaxial width W3 is greater than the fourth maximum axial width W4. Thethird maximum axial width W3 of the third teeth 42 a is preferably in arange of 2.5 mm or greater and 5.4 mm or less, and more preferably in arange of 3.0 mm or greater and 4.5 mm or less. When the third maximumaxial width W3 of the third teeth 42 a is in such a range, the thirdteeth 42 a readily engage with the outer link plate 2 a without engagingwith the inner link plate 2 b. The fourth maximum axial width W4 of thefourth teeth 42 b is preferably in a range of 1.5 mm or greater and 2.3mm or less. When the fourth maximum axial width W4 of the fourth teeth42 b is in such a range, the fourth teeth 42 b have the necessaryrigidity and readily engage with the inner link plate 2 b.

The third teeth 42 a are formed into a + (plus) shape as seen from theradially outer side, as shown in FIGS. 4, 5 and 6. The fourth teeth 42 bare formed into a − (minus) shape as seen from the radially outer side.The third teeth 42 a and the fourth teeth 42 b are formed tapering so asto gradually decrease in axial width toward the radially outer side. Thethird teeth 42 a and the fourth teeth 42 b thereby engage more readilywith the outer link plate 2 a and the inner link plate 2 b.

At least some of the third teeth 42 a and the fourth teeth 42 b aredisposed alternately in the circumferential direction, i.e. adjacent toeach other, and in the first embodiment all of these teeth are disposedin this manner as shown in FIG. 6.

The second shifting area 44 includes the second shifting teeth 42 c,which are provided to at least one of the teeth 42. The second shiftingteeth 42 c are an example of shifting teeth. In the first embodiment, aplurality (e.g., two) of second shifting teeth 42 c is provided. Thesecond shifting teeth 42 c are provided at intervals in thecircumferential direction. The second shifting teeth 42 c have secondguide surfaces 42 d for guiding the chain 2 in a first surface 16 a (seeFIG. 6) side and a second surface 16 b (see FIG. 4) side of the secondsprocket 16, as shown in FIGS. 4 and 6. The second guide surfaces 42 dare an example of a guide surface. The first surface 16 a of the secondsprocket 16 is the front surface disposed on the axially outer sidefarther from the bicycle frame when the crank assembly 10 is mounted tothe bicycle, and the second surface 16 b is the rear surface disposed onthe axially inner side nearer to the bicycle frame. The second guidesurfaces 42 d are formed as being recessed so as to gradually decreasein thickness toward the sides of the second shifting teeth 42 c.

In the first embodiment, the second shifting area 44 may contain theprotuberances or concave part of the first shifting area 34. However,the second shifting area may also contain only the protuberances or onlythe concave part.

Shifting Action in Crank Assembly

In the bicycle crank assembly 10 having such a configuration, when theup shifting action from the second sprocket 16 to the first sprocket 14is performed by a front derailleur (not shown), the bicycle crankassembly 10 is rotated in the advancing rotational direction R. In thisstate, when the front derailleur moves from a position facing the secondsprocket 16 to a position facing the first sprocket 14, the chain 2separates from the teeth of the second sprocket 16. Having separatedfrom the second sprocket 16, the chain 2 is supported on the secondprotuberance 36 b and moved to the radially outer side, and is alsosupported on the first protuberance 36 a and guided to the teeth 32 ofthe first sprocket 14. At this time, the chain 2 is guided to the firstprotuberance 36 a by the concave part 38 of the first shifting area 34.Therefore, the chain 2 supported on the second protuberance 36 b isreliably supported on the first protuberance 36 a.

When a down shifting operation from the first sprocket 14 to the secondsprocket 16 is performed by the front derailleur (not shown), thebicycle crank assembly 10 is rotated in the advancing rotationaldirection R. In this state, when the front derailleur moves from aposition facing the first sprocket 14 to a position facing the secondsprocket 16, the chain 2 separates from the teeth of the first sprocket14. Having separated from the first sprocket 14, the chain 2 is guidedtoward the teeth 42 of the second sprocket 16 and engaged with the teeth42.

Second Embodiment

In the first embodiment, the bicycle crank assembly 10 has a firstsprocket 14 and a second sprocket 16, but the crank assembly 110 of thesecond embodiment further comprises a third sprocket 18 in addition tothe first sprocket 14 and the second sprocket 16, as shown in FIG. 7.The third sprocket 18 has fewer teeth than the second sprocket 16. Thefirst sprocket 14 and the second sprocket 16 have the sameconfigurations as the first embodiment and are therefore denoted in FIG.7 by the same symbols and are not described.

Third Sprocket

The third sprocket 18 has a rotational center axis Z, and comprises athird sprocket main body 50, a plurality (e.g. 20 to 30) of teeth 52disposed along the circumferential direction on the radially outer sideof the third sprocket main body 50, and a third shifting area 54, asshown in FIG. 8. The third sprocket main body 50 is an example of asprocket main body. The third shifting area 54 is an example of ashifting area. The third sprocket main body 50 and the teeth 52 are madeof metal and are formed integrally. The third sprocket main body 50 hasa plurality (e.g. four) of third fixed parts 50 a fixed to the secondattachment parts 24 b (see FIG. 1) of the sprocket attachment arms 24and disposed at intervals in the circumferential direction. The thirdfixed parts 50 a are configured from through-holes, and are disposed inpositions facing the plurality of second attachment parts 24 b. Thethird sprocket 18, together with the second sprocket 16, is fixed to thesprocket attachment arms 24 by the second fixing bolts 28 (see FIG. 4)threaded with the second attachment parts 24 b.

The teeth 52 include at least one fifth tooth 52 a having a fifthmaximum axial width W5 (see FIG. 5), and at least one sixth tooth 52 bhaving a sixth maximum axial width W6. The fifth teeth 52 a are formedso as to be capable of engaging with the outer link plate 2 a of thechain 2. The sixth teeth 52 b are formed so as to be capable of engagingwith the inner link plate 2 b of the chain 2. The fifth maximum axialwidth W5 is greater than the sixth maximum axial width W6. The fifthmaximum axial width W5 of the fifth teeth 52 a is preferably in a rangeof 2.5 mm or greater and 5.4 mm or less, and more preferably in a rangeof 3.0 mm or greater and 4.5 mm or less. When the fifth maximum axialwidth W5 of the fifth teeth 52 a is in such a range, the fifth teeth 52a readily engage with the outer link plate 2 a without engaging with theinner link plate 2 b. The sixth maximum axial width W6 of the sixthteeth 52 b is preferably in a range of 1.5 mm or greater and 2.3 mm orless. When the sixth maximum axial width W6 of the sixth teeth 52 b isin such a range, the sixth teeth 52 b have the necessary rigidity andreadily engage with the inner link plate 2 b.

The fifth teeth 52 a are formed into a + (plus) shape as seen from theradially outer side, as shown in FIGS. 5 and 8. The sixth teeth 52 b areformed into a − (minus) shape as seen from the radially outer side. Thefifth teeth 52 a and the sixth teeth 52 b are formed tapering so as togradually decrease in axial width toward the radially outer side. Thefifth teeth 52 a and the sixth teeth 52 b thereby engage more readilywith the outer link plate 2 a and the inner link plate 2 b.

At least some of the fifth teeth 52 a and the sixth teeth 52 b aredisposed alternately in the circumferential direction, i.e. adjacent toeach other, and in the first embodiment all of these teeth are disposedin this manner as shown in FIG. 8.

The third shifting area 54 includes third shifting teeth 52 c, which areprovided to at least one of the teeth 52. In the second embodiment, aplurality (e.g., two) of third shifting teeth 52 c is provided. Thethird shifting teeth 52 c are provided at intervals in thecircumferential direction. The third shifting teeth 52 c have thirdguide surfaces 52 d for guiding the chain 2 in a first surface 18 a (seeFIG. 8) side and a second surface (not shown) side of the third sprocket18, as shown in FIG. 8. The third guide surfaces 52 d are an example ofa guide surface. The first surface 18 a of the third sprocket 18 is thefront surface disposed on the axially outer side farther from thebicycle frame when the crank assembly 10 is mounted to the bicycle, andthe second surface is the rear surface disposed on the axially innerside nearer to the bicycle frame. The third guide surfaces 52 d areformed as being recessed so as to gradually decrease in thickness towardthe sides of the third shifting teeth 52 c.

In the third embodiment, the third shifting area 54 may contain theprotuberances or concave part of the first shifting area 34. However,the third shifting area may also contain only the protuberances or onlythe concave part.

OTHER EMBODIMENTS

Embodiments of the present invention are described above, but thepresent invention is not limited to these embodiments; variousalterations can be made within a range that does not deviate from thescope of the invention. Particularly, the plurality of embodiments andmodifications disclosed in the specification and be arbitrarily combinedas necessary.

(a) The first and second embodiments give a front sprocket as an exampleof a bicycle sprocket, but the present invention is not limited as such.The present invention can also be applied to a rear sprocket.

(b) In the bicycle crank assembly of the first and second embodiments,first teeth and second teeth having different axial widths are providedto all of the sprockets, but the present invention is not limited assuch. Any sprocket (e.g. the second and/or third sprocket, small indiameter) may be configured from second teeth alone.

(c) In the first and second embodiments, the first teeth were formedinto + shapes or T shapes as seen from the radially outer side, but thepresent invention is not limited as such. These teeth may also be formedinto other shapes such as diamonds, trapezoids, triangles, and hexagons.

(d) In the first and second embodiments, the first shifting area 34 hasthe second protuberance 36 b, but a second protuberance 36 b need not beprovided.

(e) In the first and second embodiments, there are four sprocketattachment arms 24, but the number of sprocket attachment arms is notlimited to four.

(f) In the first and second embodiments, the sprocket main bodies andthe pluralities of teeth are formed integrally, but the presentinvention is not limited as such. The sprocket main bodies and thepluralities of teeth may be formed separately. The pluralities of teethmay be made of metal, for example, and the sprocket main bodies may bemade of a synthetic resin such as a carbon fiber reinforced resin or adifferent metal than the teeth, for example (a light metal such asaluminum, for example), to reduce weight.

(g) The shifting areas of the sprockets may include the − (minus) shapedsecond teeth 32 b, fourth teeth 42 b, and sixth teeth 52 b.

Also, it will be understood that although the terms “first” and “second”may be used herein to describe various components these componentsshould not be limited by these terms. These terms are only used todistinguish one component from another. Thus, for example, a firstcomponent discussed above could be termed a second component and viceversa without departing from the teachings of the present invention.

While only selected embodiments have been chosen to illustrate thepresent invention, it will be apparent to those skilled in the art fromthis disclosure that various changes and modifications can be madeherein without departing from the scope of the invention as defined inthe appended claims. Thus, the foregoing descriptions of the embodimentsaccording to the present invention are provided for illustration only,and not for the purpose of limiting the invention as defined by theappended claims and their equivalents.

What is claimed is:
 1. A multiple bicycle rear sprocket assemblycomprising: a first sprocket including a first sprocket body, aplurality of first sprocket teeth, and at least one first shifting area,the plurality of first sprocket teeth being disposed along acircumferential direction on a radially outer side of the first sprocketbody, the plurality of first sprocket teeth including at least one firsttooth having a first maximum axial width for engaging with an outer linkplate of the chain, and at least one second tooth having a secondmaximum axial width for engaging with an inner link plate of the chain,the first maximum axial width being larger than the second maximum axialwidth; and a second sprocket including a second sprocket body and aplurality of second sprocket teeth, the second sprocket being smallerthan the first sprocket, the second sprocket teeth being disposed alonga circumferential direction on a radially outer side of the secondsprocket body, the second sprocket teeth being configured fromadditional second teeth only, the additional second teeth beingconfigured for engaging with the inner link plate of the chain, thefirst maximum axial width being larger than a maximum axial width ofeach of the additional second teeth.
 2. The multiple bicycle rearsprocket according to claim 1, wherein the at least one first toothincludes a plurality of first teeth.
 3. The multiple bicycle rearsprocket according to claim 1, wherein the at least one second toothincludes a plurality of second teeth.
 4. The multiple bicycle rearsprocket according to claim 1, wherein the at least one first tooth isformed into a T shape as seen from the radially outer side.
 5. Themultiple bicycle rear sprocket according to claim 1, wherein the firstmaximum axial width of the first teeth is in a range of 2.5 mm orgreater and 5.4 mm or less.
 6. The multiple bicycle rear sprocketaccording to claim 1, wherein the second maximum axial width of thesecond teeth is in a range of 1.5 mm or greater and 2.3 mm or less. 7.The multiple bicycle rear sprocket according to claim 1, wherein themaximum axial width of the additional second teeth is in a range of 1.5mm or greater and 2.3 mm or less.
 8. The multiple bicycle rear sprocketaccording to claim 7, wherein the first maximum axial width of the firstteeth is in a range of 2.5 mm or greater and 5.4 mm or less.
 9. Themultiple bicycle rear sprocket according to claim 1, wherein the atleast one first tooth is formed into a T shape as seen from the radiallyouter side.
 10. The multiple bicycle rear sprocket according to claim 1,wherein the at least one shifting area includes a plurality of theshifting areas.